Fluke 45 - Manual (Page 70)

Operating the Meter Using the Computer Interface
How the Meter Processes Output
5
5-11
How the Meter Processes Output
The following paragraphs summarize how the meter processes output. The meter outputs
an alphanumeric string in response to a query command from the host. (Query commands
are easily identified because they all end with "?".) An output string is terminated by a
Carriage Return and Line Feed (<CR><LF>) for RS-232 applications or a Line Feed with
End or Identity (<LF><EOI>) for IEEE-488.
After sending the meter a command via the RS-232 interface, wait for the meter to return
a prompt before sending another command. If you do not do so, a device-dependent
command error is generated, and the second string is discarded.
If the meter is part of an IEEE-488 bus system, the output data is not actually sent onto
the bus until the host addresses the meter as a talker. When the output buffer is loaded,
the Message Available (MAV) bit in the Status Byte Register is set true. (For more
information, see "Status Byte Register" later in Chapter 5.)
Numeric output from the meter is displayed as shown in the following examples:
EXAMPLE EXPLANATION
+1.2345E+0 Measured value of 1.2345
+1.2345E+6 Measured value of 1.2345 x 10 6
+12.345E+6 OHM Measured value of 12.345 x 10 6 ohms (format 2)
+lE+9 Positive overload (OL on the display).
-1E+9 Negative overload (OL on the display).
Triggering Output
The meter takes measurements when it is triggered to do so. The five trigger types
available on the meter (see Table 5-3) fall into two basic categories:
•
An "internal trigger" triggers measurements continuously.
•
An "external trigger" triggers a measurement only at the direction of the user.
A measurement can be externally triggered in four ways:
•
External trigger with rear trigger disabled (Trigger type "2" or "3" from Table 5-3).
See "External Triggering from the Front Panel", below.
•
External trigger with rear trigger enabled (Trigger type "4" or "5" from Table 5-3).
See "External Triggering via the Computer Interface", below.
•
IEEE-488.1 GET command
•
IEEE-488.2 *TRG command (see Table 5-8).
External Triggering from the Front Panel
To enable an external trigger and trigger a measurement from the front panel, perform the
following procedure:
1. Make sure that the RS-232 interface is enabled by pressing
S, then R: the RS-
232 interface is enabled if "baud" and a baud rate are displayed.
If the RS-232 interface is enabled, press any button but
E, U, or T .
If the RS-232 interface needs to be enabled, refer to the procedure under "Setting
Communication Parameters (RS-232)" earlier in Chapter 5.